tutorial/tour: minor text and formatting changes

[Lekensteyn]

The picture says "Start Build", not "Force Build" (that is the old UI).

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Other issues in the tutorial that are not addressed here:

• Had to use virtualenv --python=python2 since Python 3 apparently does not work yet, but pip install buildbot[bundle] fails with a strange error (Please install buildbot, buildbot_pkg, and mock modules in order to install that package, or use the pre-build .whl modules available on pypi). Reported before in Specify Python Version buildbot-website#10.
• FirstRun refers to virtualenv "bb-master", but the follow-up uses "sandbox"
• outdated pictures (using old web UI)
• IRCBot example does not work, apparently it got moved from .status to .reporters and needs to be added to c['reporters'] instead of c['status'].
• Text mentions a login, but the Force Build option can be used without. The example configuration does not contain the authorization configuration mentioned in the tutorial.

[mention-bot]

@Lekensteyn, thanks for your PR! By analyzing the history of the files in this pull request, we identified @sa2ajj, @winksaville and @lsblakk to be potential reviewers.

[sa2ajj]

let's see what automatic checks say...

[sa2ajj]

@Lekensteyn thank you for the PR, the other things you mentioned are really worth a PR that we'd appreciate very much!